1 Long before astronauts traveled into space, people had to guess about Earth's shape. Some thought it was flat. Others thought it was a disc. However, no one had real proof about its shape. That is until ancient Greek geographers came along. They were some of the first scientists to figure out the shape of our planet. These geographers used mathematics and their observations to design the first globes. These globes were our first models of Earth.2 Earth has a geographical grid. It is important to learn about this grid so that you can understand globes. This grid is found on flat maps and on globes. It is a pattern of horizontal and vertical lines. These lines intersect at coordinates. Geographers use these coordinates to locate places on Earth, on maps, and on globes. The vertical lines are called lines of longitude or meridians. Lines of latitude or parallels are the horizontal lines.3Hipparchus was a Greek geographer. He was born in 150 B.C. Hipparchus divided Earth into 360 sections. These sections are called degrees. These sections were drawn on the globe to show lines of longitude. Meridians run from pole to pole and divide the Earth vertically. In 1884, scientists created our prime meridian. It measures 0 degrees (0º) longitude and runs through Greenwich, England. If you sail up the Thames River to Greenwich, you will find the Royal Naval Observatory. This is where you will see a marker for the prime meridian.